It is known that photopolymerizable elements can be used in electrographic applications. Ingersoll U.S. Pat. No. 3,286,025, for example, relates to electrographic imaging. A photopolymerizable layer comprising a polymeric binder, an ethylenically unsaturated monomer, and a photoinitiator is imagewise exposed, the exposure creating polymerized areas of reduced conductivity. When the imagewise-polymerized layer on a conductive support is corona charged and toned or developed, a developed image is formed on the polymerized areas. Ingersoll states that multiple copies can be made and describes a procedure whereby the nonimage areas of the photopolymerized element are washed out with a solvent, the developed element is placed on an offset press and printing is accomplished by lithographic technique. Ingersoll, however, does not disclose transferring a developed image to another support.
In Riesenfeld et al. U.S. Pat. No. 4,732,831 there is described an image transfer process using a photopolymerizable electrographic element wherein the photopolymerizable layer is imagewise exposed, the exposed areas are electrostatically charged while present on a conductive support and then developed by applying an oppositely charged electrostatic developer, and the developed image is transferred to another surface. In the process of U.S. Pat. No. 4,732,831 the single photopolymer layer is imagewise exposed using a single image bearing film or phototool, then charged and developed on the same side. Such a process results in a wrong-reading image being obtained on transfer to a receptor support unless the image bearing film or phototool is so configured to provide a wrong reading latent image on the surface of the photopolymerized layer which upon transfer is inverted to form a correct reading image (See FIG. 1).
It is desired that a second image derived from a second image-bearing film such as a color separation negative be added to an imaged electrographic photopolymerizable element, so that high quality, high resolution superimposed images be obtained from toned electrographic photopolymerizable elements. It is particularly desired that such superimposed, high resolution images be obtained by using liquid electrostatic developers.
Superposition of images derived from separate image-bearing films or phototools using a single electrographic master is useful whenever multiple copies of a document or pictorial are desired in more than one version, the second version involving the addition of text or pictorial information to the original version. Applications are found wherever some additional information is to be directed to only a portion of the recipients of the documents. Examples include additions of highlighting, headlines, logos, corrections, or perhaps proprietary information.
The two-layer superposition of the present invention offers several advantages over a superposition image made by a single layer photopolymer electrographic element which had been imaged previously as described in U.S. Pat. No. 4,732,831. The two-layer superposition is applicable to optically positive as well as negative-working systems. Also, the superposition of electrographic photopolymerizable elements can be done by lamination directly in a hardcopy output device, after prints have been made from the first image-bearing layer and off-line imagewise exposure of the second layer.
An additional feature of the present invention is that the charge decay rates of the two photopolymerizable layers can be different from one another so that the superimposed developed image derived from the image of the second layer can be of a different color from that of the first developed image derived from the image of the first layer. This 2-color image can be accomplished by charging the layered photopolymerizable composition with a single scorotron in a single pass followed by sequentially developing with two differently colored developers. Any combination of the two developers can be used to emphasize headlines, logos, highlights and the like with a second color, differing from the color of the basic document.